Various aspects of macrophage interactions with ocular and other cells were examined. (1) "Activated" macrophages, which are a major component of inflammatory reactions, may affect the metabolism of surrounding tissues. This damaging effect was further studied by using lens epithelial cells as the target. Of importance is the finding that prostaglandins regulate this macrophage activity, without acting directly as the damaging mediators. (2) Two macrophage-made mediators which have similar properties are interleukin 1, which activates lymphocytes, and a factor that stimulates fibroblasts. The possibility that these two factors are identical was previously proposed and supported by some preliminary data. This notion has been further supported by a series of experiments showing that the two mediators have multiple identical physical and biochemical properties. (3) Interleukin 1, which mediates certain immune responses, has been used to examine the mode of action of a newly introduced immunosuppressive drug, cyclosporin A. The drug was found to inhibit strongly certain responses mediated by interleukin 1, but to have minimal effect on other responses stimulated by this mediator.